Vitamin B.sub.12 is an essential nutrient factor required for human and animals in a minute amount. In mammals, it is contained relatively abundantly in the liver. Neither animals nor plants can biosynthesize this vitamin, which can be produced only by microorganisms. As a disease due to a lack of vitamin B.sub.12 , pernicious anemia is particularly representative thereof, and megaloblastic hemopoiesis, methylmalonic acid uria, homocystinuria, and neuropathy, etc., are caused thereby. When absorbed into the body, vitamin B.sub.12 is converted to a metabolically active vitamin B.sub.12 coenzyme (adenosylcobalamin) and methylcobalamin; the former functioning as a coenzyme in an enzymatic reaction accompanied by a movement of hydrogen, such as methylmalonyl CoA mutase, and the latter functioning as a coenzyme in an enzymatic reaction accompanied by a movement of a methyl group, such as methionine synthetase. Particularly, methylcobalamin functions in a C.sub.1 metabolism involving a folic acid coenzyme, thereby participating indirectly in a biosynthesis of thymidylic acid and playing an important role in cell growth. Accordingly, a compound exhibiting an antagonistic activity against the vitamin B.sub.12 group, i.e., a vitamin B.sub.12 antagonist, may be considered to suppress or inhibit cell growth by interfering with the DNA synthesis, and to be effective as an antitumor agent (anticancer agent) against tumor cells (cancer cells). Also, the vitamin B.sub.12 group is important for the growth of microorganisms, and the vitamin B.sub.12 antagonist is considered to have an activity as an antimicrobial agent. Conversely, the vitamin B.sub.12 antagonist may be considered to be applied for screening a microorganism mutant strain having a high vitamin B.sub.12 productivity, with a resistance thereto as the index.
In the prior art, various vitamin B.sub.12 derivatives have been synthesized and, for example, it is known that the vitamin B.sub.12 derivatives synthesized chemically or microbiologically from cobyric acid and having the isopropanolamine moiety (--NHCH.sub.2 CH(CH.sub.3)O--) converted to, for example, --NHCH(CH.sub.3)CH.sub.2 O--, --NHCH.sub.2 CH.sub.2 CH.sub.2 O--, --NHC(CH.sub.3).sub.2 CH.sub.2 O--, --NHCH.sub.2 CH(C.sub.6 H.sub.5)O-- or --NHCH.sub.2 CH(CH.sub.2 F)O--, exhibit an antagonistic activity against Escherichia coli 113-3 and Lactobacillus leichmannii (Friedrich, Vitamin B.sub.12 und verwandte Corrinoid (Georg Thieme Verlag, Stuttgart), p. 289-308, 1975). Also, cobalt-free corrinoid isolated from a microorganism, or a different kind of metal corrinoid in which, for example, rhodium, copper, and zinc, are introduced into a cobalt-free corrinoid, is known to exhibit a similar antagonistic activity against the above-mentioned microorganisms (Friedrich, Vitamin B.sub.12 und verwandte Corrinoid (Georg Thieme Verlag, Stuttgart), p. 289-308, 1975, and Copenhagen, B.sub.12 (John Wiley & Sons, New York), vol. II, p. 105-149, 1982).
Nevertheless, the preparation of cobyric acid is complicated and it is difficult to obtain same in a large amount, and when a microorganism is used, a problem arises in practical application due to the isolation thereof.
Also, vitamin B.sub.12 derivatives having a bromine or nitro group introduced into the C-10 position of the corrin ring, and vitamin B.sub.12 derivatives in which the surrounding side chains of the corrin ring are derivatized to, for example, carboxyl group, ethylamide, anilide, and hydrazide, have been chemically synthesized (Friedrich, Vitamin B.sub.12 und verwandte Corrinoid (Georg Thieme Verlag, Stuttgart), p. 289-308, 1975), but these derivatives are still unsatisfactory due to a low antagonistic activity thereof.
Accordingly, there is a need for a vitamin B.sub.12 antagonist having an excellent antagonistic activity, and which can be supplied in a large amount.